The present invention relates to a rolling bearing with a sealing device, and more particularly to a rolling bearing with a sealing device having improved characteristics in a seal fitting groove of an outer ring and a mounting portion of the sealing device to be fitted in the seal fitting groove.
With respect to conventional rolling bearings, a lubricant such as a grease or a lubricating oil is applied on raceway surfaces of an inner ring and an outer ring and rolling surfaces of rolling elements such as balls or rollers, for maintaining lubricity for a long period of time. The conventional rolling bearings include a rolling bearing with a sealing device that prevents the lubricant in a space defined by in the raceway surfaces and rolling surfaces from leaking and avoiding adhesion of dusts to these surfaces.
FIG. 5 shows one example of the rolling bearing with the sealing device. FIG. 5 shows cross sectional view of elemental portions of a single-row deep groove ball bearing with a sealing device 50 (called as xe2x80x9cball bearingxe2x80x9d hereafter). As shown in FIG. 5, the ball bearing 50 has a plurality of rolling elements 54 that are rotatably held by a retainer 53 and equidistantly arranged between an inner ring 51 and an outer ring 52 in a peripheral direction of the ball bearing 50.
The inner ring 51 has a protruding portion 55 at a central portion of an outer peripheral surface thereof, that is spaced from both end portions of the outer peripheral surface in an axial direction thereof. The protruding portion 55 protrudes toward the outer ring 52 from the outer peripheral surface of the inner ring 51. An inner raceway 51a is formed into a concave shape for receiving the rolling elements 54 at the outer peripheral surface (an upper surface in the drawing) of the protruding portion 55.
The outer ring 52 has a protruding portion 56 at a central portion of an inner peripheral surface thereof, that is spaced from both end portions of the inner peripheral surface in an axial direction thereof. The protruding portion 56 protrudes toward the inner ring 51 from the inner peripheral surface of the outer ring 52. An outer raceway 52a is formed into a concave shape for receiving the rolling elements 54 at the inner peripheral surface (a lower surface in the drawing) of the protruding portion 56. Further, at the inner peripheral surface which is adjacent a side surface 52b of the protruding portion 56, a fitting groove 57 is formed to be hollowed from the both end portion of the inner peripheral surface of the outer ring 52 to outside of the ball bearing 50 in a radius direction of the outer ring 52.
An annular sealing device 70 is substantially composed of a mounting portion 71 arranged at a outer edge portion of the sealing device 70, a lip portion 72 arranged at an inner edge portion of the sealing device 70 and a connecting portion 73 connecting the mounting portion 71 with the lip portion 72. The mounting portion 71 of the sealing device 70 is fitted into the fitting groove 57 of the outer ring 52. Then the lip portion 72 of the searing device 70 is set on a side surface 51b of the protruding portion 55 of the inner ring 51, so that the sealing device 70 is attached to the side surface of the ball bearing 50 in such manner of being secured to the outer ring 52. The sealing device 70 may be secured to either of the inner ring or the outer ring. Generally the sealing device is secured to the outer ring.
As a material composing the sealing device 70, a metal which forms the whole sealing device 70 are known, or others composed of a connecting portion formed with a metal ring, and a mounting portion and a lip portion formed with a soft rubber is also known. A sealing device formed with plastic or elastomer is also known (called as xe2x80x9cplastic sealing devicexe2x80x9d hereafter). For example, Japanese Patent Unexamined Publication No. Hei.6-313436 teaches a plastic sealing device which uses a comparatively hard synthetic-plastic-polymer at a connecting portion and a comparatively soft elastic-synthetic-plastic at a mounting portion and a lip portion, and unifies both of the plastic as one body by insert molding. In Japanese Utility Model Laid-Open No. Hei. 5-96549, another plastic sealing device which is formed by changing kinds of resins for heightening rigidity of a connecting portion and increasing flexibility of a lip portion than that of a mounting portion is described.
A plastic sealing device which is formed with a plastic simplex and has variously designing shapes of a mounting portion is also known. For example, Japanese Utility Model Laid-Open No. Hei. 4-87022 discloses, a plastic sealing device having, at an outside surface of an outer peripheral edge portion, a thin triangular shaped annular protruding portion in cross section. The annular protruding portion almost rectangular contacts with an outside surface of a fitting groove in a bending state. Further, in Japanese Utility Model Laid-Open No. Hei. 6-35662 discloses a plastic sealing device having a trapezoidal shaped protruding portions in cross section and a thin and annular protruding portion is described. An inside surface of an outer peripheral edge portion of the trapezoidal shaped protruding portion contacts an inside surface of a fitting groove of the outer peripheral edge portion. The thin and annular protruding portion contacts with an outside surface of the fitting groove in a bending condition. The trapezoidal shaped protruding portions and the thin and annular protruding portion are divided into a plurality pieces equidistantly following a peripheral edge.
In addition, as the kinds of plastics, engineering-plastic-simplex, or plastic composite materials comprising short fiber of glass fiber and carbon fiber which are mixed to be strengthened is used.
As mentioned above, since the mounting portion of the plastic sealing device is pushed into the fitting groove of the outer ring under the elastically deformed condition, a creep deformation may be caused due to atmospheric temperature or heating with rotation of the rolling bearing. Accordingly, there is a possibility that fixing force of the mounting portion into the fitting groove is reduced.
As coefficient of linear expansion of plastic is larger than that of metal, when the temperature rises, the mounting portion expands in a radial direction of the rolling bearing. Then since the amount of elastic deformation (tightening force) becomes larger than an amount of that at room temperatures, the creep deformation is easier to occur.
When an atmospheric temperature is higher than 80xc2x0 C., the plastic sealing device causes the creep deformation in almost all cases, then when the atmosphere temperature turns back to the room temperatures, a gap is possibly formed between the fitting groove of the outer ring and the mounting portion of the plastic sealing device. In addition, at that time, the fixing force becomes weak, then play or backlash may be occurred. When the fixing force into the fitting groove is reduced, slipping may be occurred between the outer ring and the plastic sealing device, so that a sealing efficiency of the plastic sealing device is lowered.
If thickness of the mounting portion is made large for heightening rigidity of the plastic sealing device, there is also such a problem that when the plastic sealing device expands in the radial direction, the expanded portion cannot be absorbed with only deformation of the mounting portion, so that the plastic sealing device itself curves outward from the side of the rolling bearing and a portion of the curve projects from the rolling bearing. In an ultra miniaturized rolling bearing having an outer radial of the outer ring being around several mm, a problem is to decrease circularity.
Rolling bearings are often served at atmospheric temperatures of 80 to 120xc2x0 C., the plastic sealing device cannot fully cope with services for a long period of time, because the plastic sealing device is easy to cause the creep deformation at the atmospheric temperatures regardless of changes of measures such as the above engineering-plastic-simplex, or composite materials comprising short fiber of glass fiber and carbon fiber which are mixed to be strengthened, and only plastic sealing device varying (devising) shapes of the mounting portion.
The present invention has been established in view of these circumstances, and an object of the invention is to offer a rolling bearing with a sealing device which can be used at high atmospheric temperatures, prevents the mounting portion of the sealing device from creep deformation, and maintains the sealing efficiency for a long time.
The object of the invention is accomplished by a rolling bearing with a sealing device which includes an inner ring, an outer ring having a fitting groove formed as a concave shape portion that comprises an outside surface, an inside surface and a bottom face at vicinity of an edge portion of the inner peripheral surface of the outer ring in an axial direction of the rolling bearing, wherein the fitting groove becomes narrower, in cross section, as going to an outside in a radius direction of the rolling bearing, the outside surface is formed at edge side of the inner peripheral surface of the outer ring and tilts at a tilt angle of 5 to 30 degrees with respect to the radial direction of the rolling bearing, the inside surface is formed on opposite side to the outside surface and tilts at a tilt angle with respect to the radial direction smaller than the tilt angle of the inside surface, the bottom face connects the outside surface and the inside surface and a total of these tilt angles of the outside surface and the inside surface is 35 degrees or more, a plurality of rolling elements rotatably arranged between the inner ring and the outer ring, and an annular sealing device arranged at a side of the rolling bearing and having a mounting portion that is fitted within the fitting groove and formed at an outer peripheral edge portion of the annular sealing device, wherein the mounting portion of the sealing device has a base portion contacting the inside surface of the fitting groove and a projecting portion protruding toward the outside surface of the fitting groove from the base portion, the projecting portion reduces thickness in such a manner that a front end portion of the projecting portion becomes the thinnest in the projecting portion.
Herein, the front end portion of the projecting portion is meant by a front end portion of the projecting portion contacting the outside surface of the fitting groove.
According to the above rolling bearing with the sealing device of such a structure, even if the rolling bearing is used at a high temperature and the sealing device is expanded, since a tilt angle of the outside surface and inside surface of the fitting groove of the outer ring is small as 5 to 30 degrees in the radial direction of the rolling bearing, a distortion of the projecting portion of the sealing device (called as xe2x80x9cexposed threadxe2x80x9d hereafter) is restrained to be a little increase. Therefore, when the atmosphere temperature turns back to the room temperature, the front end portion of the projecting portion suppresses deterioration with the fitting condition in the fitting groove owing to stress relaxation in the mounting portion of the sealing device.
Even if the atmosphere temperature turns back to the room temperature after the mounting portion is creep-deformed by somewhat stress relaxation, and the expansion of the sealing device in the radial direction is settled down. Since the tilt angle of the fitting groove is small and a dimensional change in the width direction is small with respect to a dimensional change in the radial direction, the exposed thread can be maintained and the sealing efficiency can be kept preferable without generating a gap between the mounting portion and the fitting groove.
Besides, since the projecting portion of the sealing device becomes thinner toward the outside surface of the fitting groove and the front end portion of the projecting portion contacting the outside surface becomes a thinner than another portion of the projecting portion, even if the sealing device expands in the radial direction, the outer peripheral edge portion of the sealing device can escape into an inner portion of the fitting groove at low force. Then, owing to the coefficient of linear expansion of plastic larger than that of metal, even if the sealing device expands in the radial direction and the exposed thread is made larger than that of state at the room temperature, the sealing device does not project from the side of the bearing because a remaining power does not load on the other portions of the sealing device.
In an embodiment of the present invention, it is preferable that the inner ring has a sealing groove formed into a concave shape in an axial direction, the sealing groove comprises a bottom face connecting a inside surface and a outside surface at vicinity of a edge portion of the inner peripheral surface of the outer ring, and the inside surface opposites to the outside surface; and the sealing device has a lip portion formed on an inner peripheral edge portion of the sealing device and contacts two portions that are the inside surface of the sealing groove and a vicinity of a central portion of the outer peripheral surface of the inner ring more inside than the sealing groove, to thereby form a labyrinth.
With this construction, in the rolling bearing with the sealing device, the lip portion of the sealing device contacts the two pats which are the sealing groove defined in the inner ring and the central portion of the outer peripheral surface of the inner ring, so that the sealing efficiency of the sealing device of the inner ring side is improved.